1. Field of the Invention
The present invention relates to explosive compositions comprising a sensitized blend of a water-in-oil emulsion and solid particulate inorganic oxidizing salt, preferably ammonium nitrate (AN).
2. Description of the Prior Art
Explosives which comprise a blend of a water-in-oil emulsion and solid particulate AN, e.g., ANFO (AN prills coated with fuel oil), are becoming increasingly popular with blasters owing to the fact that they are able to offer the advantages of high bulk density and blasting energy characteristic of emulsion explosives, while at the same time resulting in cost reductions owing to the lower cost of the AN. In some instances, however, these blend explosive produces, referred to herein as "emulsion blend explosives", have been found to have a short shelf life, requiring the use of the products immediately after they have been formed. "Short shelf life" means that an explosive product lacks stability, undergoing deleterious changes(s) in structure and/or composition to the degree that it cannot be depended upon to detonate at the required velocity at the required time. If the product's shelf life is very short, it almost certainly is unsuitable for use in packaged form, and can be unsuitable for use in bulk form, especially if it needs to be transported to the place of use or allowed to stand in a borehole for some time after loading.
U.S. Pat. No. 4,555,278, issued Nov. 26, 1985, to L. A. Cescon and N. J. Millet, Jr., describes the formation of emulsion blend explosives having improved storage stability. This application states that in these explosives, the blend-destabilizing transport or loss of water from the emulsion's aqueous dispersed phase across the continuous oil phase to the admixed nitrate particles is minimized by virtue of a barrier or medium, resistive to water-transport, formed preferably by the continuous emulsion phase itself, e.g., by the presence of an anionic emulsifying system comprising a fatty acid salt and a free fatty acid, the latter in solution in an oil as the continuous emulsion phase. The same patent application further states that a water-transport-resistive barrier also can be provided, for example, by a low-diffusivity (to water) coating on the nitrate particles.
One of the materials which is commonly employed as the particulate solid component of emulsion blend explosives in ANFO. While ANFO is a popular blasting product in its own right because of economy and convenience, its lack of water resistance and low product density are well-recognized as product deficiencies. The blending of ANFO with a water-in-oil emulsion results in a product of higher density, and a certain degree of water resistance may be achieved in the blend product, especially if the emulsion/solids weight ratio is high. Thus, some unpackaged emulsion blend products can be used in wet boreholes. Nevertheless, even those emulsion blend explosives which are storage-stable could be utilized in a more economic manner, i.e., in bulk form with formulations of high solids content, if their water resistance could be improved.